How to fix error "Error mapping types" in AutoMapper?

Question

I have these two classes which were reverse engineered (scaffolded) with EF Core:

public partial class TblA
{
    public TblA()
    {
        TblBs = new HashSet<TblB>();
    }

    public string TenantId { get; set; }
    public int Id { get; set; }
    
    public virtual ICollection<TblB> TblBs { get; set; }
}

public partial class TblB
{
    public string TenantId { get; set; }
    public int Id { get; set; }
    public string Value { get; set; }

    public virtual TblA A { get; set; }
}

Now, I am trying to use AutoMapper to map an object of class TblA into an object of class A. This is how class A is defined in my project:

public class A
{
    public string TenantId { get; set; }
    public int? Id { get; set; }
    public List<B> Bs { get; set; }
}

public class B
{
    public string TenantId { get; set; }
    public int Id { get; set; }
    public string Value { get; set; }
}

This is how my map is defined:

CreateMap<TblA, A>()
    .ForMember(dest => dest.Bs, opt => opt.MapFrom(src => src.TblBs))
    .ReverseMap()

In my project, I am creating an object of class TblA which I then add to the database via AddAsync() and SaveChangesAsync(). Then, I try to map this object to class A via Map<A>(entity) where entity is the object which I also passed to AddAsync(). Right after calling Map<A>(entity), I get this error:

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      AutoMapper.AutoMapperMappingException: Error mapping types.

      Mapping types:
      TblA -> A
      <namespace>.TblA -> <namespace>.A

      Type Map configuration:
      TblA -> A
      <namespace>.TblA -> <namespace>.A

      Destination Member:
      Bs

       ---> AutoMapper.AutoMapperMappingException: Error mapping types.

      Mapping types:
      TblB -> B
      <namespace>.TblB -> <namespace>.B

      Type Map configuration:
      TblB -> B
      <namespace>.TblB -> <namespace>.B

      Destination Member:
      TenantId
       ---> System.NullReferenceException: Object reference not set to an instance of an object.
        at lambda_method734....

I have thoroughly inspected the object before mapping it and the TenantId is set just fine to a valid string value. Therefore, I do not understand where this error is coming from because the TenantId is not null. What could be the problem here?